<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <h2>来到了b页面</h2>
    <button class="back">回退</button>
</body>
<script>
    const back=document.querySelector('.back')
    back.onclick=function() {
        console.log(history.length)
        history.go(-1)
    }
</script>
</html>